While studying ammonia synthesis over a porous nanoscopic Ru/CeO2 catalyst enhanced by a surface protonic electrical current at 2-400°C, we discovered the onset of a plasma-like discharge and ammonia production at nominal furnace temperatures below 140°C and above DC currents of around 3 mA through the 0.8 cm2 catalyst bed. The plasma-like behaviour was characterised by a constant power of around 2.5 W, i.e. in current controlled mode in the range 3-5 mA, the voltage varied in the range 800–500 V DC inversely with the current (apparent negative resistance). The temperature of the catalyst bed was read with a thermocouple in a protrusion of the quartz wall into the bed, and the plasma-like behaviour and ammonia production had a sharp onset below 170°C and was operative down to around 100°C of catalyst temperature. There were no associated visible light phenomena. The product ammonia contents were in the range of 1000 ppm, and remarkably, it was faradaic, i.e. proportional to the current, corresponding roughly to between 1 and most often 3 electrons per NH3, depending on conditions. The experiments were performed in a high-voltage high-pressure version of a NorECs ProboStat heated in a tubular furnace and equipped with a NorECs quartz fixed-bed accessory including gold electrodes and 3 thermocouples (outside, inside, and under the catalyst). It was fed with N2+3H2 at 1-10 bar total pressure, and ammonia yield was analysed with a GC. The electrical field was provided with a 0-10 kV maximum 5 mA DC power supply. Several aspects of the observations remain unexplained and require further investigations. It seems clear that the process has no prospect of commercial utilisation, since the electrical power consumed for the plasma is unacceptably high for an exothermic reaction. It is however of interest if it can be sustained in and catalyse an endothermic reaction.

Plasma-enhanced ammonia synthesis over nanoscopic Ru/CeO2

ACS Spring 2022

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.